1. Field of the Invention
This invention relates to medical articles, and more particularly, relates to a lubricating composition, a metal article coated therewith and to a method for its preparation.
2. Background of the Invention
Many occasions arise when it is necessary to puncture the skin with a metal device, generally of steel, having a sharp point or edge. Representative of such devices are surgical blades, hypodermic needles, lancets, cannulas, catheter insertion devices, guidewires, stylets and the like. In other cases, a cutting edge, such as a razor blade, is advanced across a skin surface.
When such a device is advanced across the skin or inserted through the skin, the skin is stretched and a certain amount of pain is experienced. It has been common practice for many years to lubricate the device to minimize pain.
Noncuring, nonpolar silicones, such as the DC-360.TM. series of medical grade polydimethyl siloxanes (PDMS) available from Dow Corning Co. have been used. These products, while widely used, have the disadvantage of creeping or migrating from the surface to which they have been applied. Another problem with these lubricants is adhesion which develops over time when two plastic surfaces are engaged by an interference fit. For plastic syringes, Williams et
U.S Pat. No. 4,767,414, discloses that plasma treatment of one of the surfaces and PDMS at the interface overcomes adhesion For a catheter cannula assembly, Williamitis et al. discloses in U.S. Pat. No. 4,664,657 that adhesion can be overcome if the PDMS is of high viscosity.
The problem of migration is particularly severe when metal surfaces are lubricated with noncuring PDMS. For example, in the case of a hypodermic needle coated with PDMS, the coating may be substantially removed due to frictional forces during penetration of the skin and vein, making subsequent removal of the needle difficult and painful to the patient. Migration during storage and inadvertent removal during processing is also a concern.
Spielvogel, in U.S. Pat. No. 4,720,521, discloses overcoming the migration problem by including a noncuring PDMS in a curing composition. The noncuring lubricating PDMS is occluded in a mixture of at least three curing silicones which adhere to a metal surface.
U.S. Pat. No. 3,574,673 to Schweiger discloses curing organopolysiloxanes used as friction reducing coatings on blades. These products are copolymers of alkylamine modified methoxysiloxanes which undergo room temperature moisture curing to a gelatinous film. Representative of this class of materials is the commercially available product MDX-4-4159. Depending on ambient humidity, MDX-4-4159 requires at least a four hour precure and from two to ten days for complete cure. In addition, solvent solutions used for dip application, because of the moisture curing, quickly turn cloudy due to precipitated polymer from reaction of the MDX-4-4159 with humidity in the air. Dipping solutions must be replaced frequently which is time consuming, wasteful and costly.
In U.S. Pat. No. 4,904,433, Williamitis discloses a method for catheter tipping which includes applying a noncuring aminoalkyl terminated polysiloxane to a catheter blank, mounting the coated blank on a mandrel, advancing the mandrel into a heated die for tipping and removing the tipped catheter from the die and the mandrel.
Since conventional lubricants are not water soluble, it has been standard practice in the art to apply lubricant coatings to articles from a solvent solution. A variety of solvents has been used, most of which are either inflammable or toxic. In recent years, fluorocarbons have come to the fore as the preferred solvents. These solvents, however, are now known to be a major contributor to the depletion of the atmosphere ozone layer. Accordingly, there is a need for a polysiloxane composition capable of lubricating metal surfaces which overcomes migration problems by adhering firmly and quickly without a need for cure time and which can be applied from a safe and environmentally acceptable solvent. The present invention addresses this need.